This is a proposal for analysis of data collected in 1971 and 1973 as part of a two-wave trend and longitudinal study of changes in adolescent drug behavior and the correlates of change in a panel of 22 selected junior and senior high schools in four regions of the U.S. In these schools, nearly 33,000 students completed questionnaires in 1971 and an equal number two years later; approximately 7,000 of them were present on both occasions and are expected to be matched, although anonymous. Analysis will focus on institutional as well as on individual factors related to drug-use changes in these panels of schools and students. In addition, support is requested for experimental and comparative studies of drug use already conducted or to be conducted in other populations. These include: a special study conducted in 1973 with matched samples of 11th graders, half given questionnaires at home and the other half in school, to determine what may explain differences in reported drug use revealed in our own research and that of others between home-- and school-administered questionnaires; a comparative study of drug use in three English secondary schools; a study of drug use in a U.S. high school with a large Puerto Rican population for comparison with a study of adolescent drug use in Puerto Rico; repetition of three successive national household sample surveys of adolescent drug use which were conducted in the U.S. in 1971, 1972 and 1973.